NICMOS Narrowband Infrared Photometry of TW Hydrae Association Stars

David Weintraub, Vanderbilt University
Didier Saumon, Vanderbilt University
Joel H. Kastner, Rochester Institute of Technology
Thierry Forveille, Observatoire de Grenoble

© 2000 The American Astronomical Society

We thank the referee for thoughtful suggestions which improved the clarity of the manuscript, A. Burrows for computing the evolutionary sequences used in this work, and F. Allard, P.H. Hauschildt, I. Baraffe and G. Chabrier for making their synthetic spectra and models available. This research was supported by NSF grant AST93-18970 and NASA grants NAG5-4988 and GO07861.01-96A and is based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.ISSN:1538-4365 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.


We have obtained 1.64, 1.90 and 2.15 µm narrow-band images of five T Tauri stars in the TW Hya Association (TWA) using the Near-Infrared Camera and Multiobject Spectrometer aboard the Hubble Space Telescope. Most of the T Tauri stars in our study show evidence of absorption by H2O vapor in their atmospheres; in addition, the low-mass brown dwarf candidate, TWA 5B, is brighter at 1.9 µm than predicted by cool star models that include the effects of H2O vapor but neglect dust. We conclude that the effect of atmospheric dust on the opacity is important at 1.9 µm for TWA 5B, the coolest object in our sample. The available evidence suggests that the TWA is 5–15 MY old. Comparison of the colors of TWA 5B with theoretical magnitudes as a function of age and mass then confirms previous claims that TWA 5B is substellar with a mass in the range 0.02–0.03 M⊙. The accurate single-epoch astrometry of the relative positions and separation of TWA 5A and TWA 5B reported here should permit the direct measurement of the orbital motion of TWA 5B within only a few years (Refer to PDF file for exact formulas).